Many types of materials that are processed in an extruder can include entrapped air and/or other types of gasses. The entrapped air and/or other types of gasses can interfere with the proper processing of the materials in the extruder. Various arrangements have been developed to remove air and/or other types of gasses during the processing of materials in the extruder. Non-limiting examples of such arrangements are disclosed in U.S. Pat. Nos. 2,833,750; 2,944,047; 3,040,005; 3,156,009; 3,177,272; 3,799,234; 3,870,284; 3,985,348; 4,065,532; 4,100,244; 4,127,635; and 4,155,655, all of which are incorporated herein by reference.
Many prior art extruder systems that include a venting arrangement are used to extrude polymer materials. Polymer materials, when being extruded through the extruder, are generally in a fluid form that enables the polymer to easily flow through the extruder. Typically an opening is formed in the barrel of the extruder and gas (e.g., air, nitrogen, water vapor, etc.) is removed from extruder as the polymer is moved through the extruder. A diverter is commonly placed at or near the opening in the barrel to inhibit or prevent the polymer from flowing into the opening and plugging the opening.
It has been found that materials that are more viscous than polymers or materials that are not true liquids, such as clays, mastics, ceramics and the like have a tendency to plug the opening in the barrel even when a diverter is used. A true liquid material is defined as a material that cannot resist shear and seeks a uniform level when placed in a container. As such, standard extruder arrangements that include a venting system cannot be used with highly viscous materials or non-true liquid materials. Such materials can resist shear when being fed through an extruder arrangement and building up on and eventually clog or plug the opening in the barrel.
In view of the current state of the art of extruders, there is a need for an extruder arrangement that can be used to remove gas from the extruder when extruding various types of materials, and especially highly viscous materials or non-true liquid materials.